I asume that the two programs run in two different controllers. How did you setup the interrupts? Looking at the code for Rx, and supposing that the routine is an ISR, it will most likely deadlock: after the received byte is transmitted, TI is set, A is loaded with whatever is (still) in SBUF and again transmitted after TI is cleared, etc. The same happens in your Tx part. I don't believe that is what you want..